The present invention relates to a vehicle control system, and more specifically to a vehicle-to-vehicle distance controlling type adaptive cruise control (ACC) system capable of maintaining a proper vehicle-to-vehicle distance and a proper vehicle speed in all driving circumstances.
A Japanese Patent Provisional (Kokai) Publication No. 4-244434 discloses a conventional cruise control system. This control system includes an input or sensor section, a controller section and an output or actuator section. The output (or actuator) section includes a throttle actuator for varying the vehicle speed by varying the opening of a throttle valve for an engine. The input (or sensor) section includes a first subsection for sensing an actual vehicle speed, and a second subsection adapted to be operated by a driver to input a desired set speed. The controller section includes an ACC controller for automatically maintaining the vehicle speed at the driver's speed setting by sending a control signal to the throttle actuator to control the opening of the throttle valve. The input section further includes a third subsection including a distance measuring device, such as a laser radar, for measuring a vehicle-to-vehicle distance between the controlled vehicle and another vehicle ahead. The controller section functions to control the vehicle speed so as to sustain an adequate vehicle-to-vehicle distance. Moreover, the controller section calculates a road traffic density in accordance with the vehicle-to-vehicle distance. The controller section increases a gain for the vehicle-to-vehicle distance control when the traffic density is high, and decreases the gain when the traffic density is low. The vehicle can respond sensitively to the widely changing vehicle-to-vehicle distance when the traffic is heavy. When the traffic is sparse, the control performance is smooth and mild.